Enhanced spin-orbit torque via modulation of spin current absorption

TL;DR

This paper demonstrates that adding a Ru layer enhances spin-current absorption at the interface, significantly increasing the spin-orbit torque in HM/FM multilayers, supported by experiments and a theoretical model.

Contribution

It introduces a method to modulate spin-current absorption using Ru layers, leading to enhanced spin-orbit torque in multilayer structures.

Findings

Ru interface boosts spin-current absorption

Enhanced SOT efficiency observed with Ru layer

Theoretical model explains interface effects on SOT

Abstract

The magnitude of spin-orbit torque (SOT), exerted to a ferromagnet (FM) from an adjacent heavy metal (HM), strongly depends on the amount of spin currents absorbed in the FM. We exploit the large spin absorption at the Ru interface to manipulate the SOTs in HM/FM/Ru multilayers. While the FM thickness is smaller than its spin dephasing length of 1.2 nm, the top Ru layer largely boosts the absorption of spin currents into the FM layer and substantially enhances the strength of SOT acting on the FM. Spin-pumping experiments induced by ferromagnetic resonance support our conclusions that the observed increase in the SOT efficiency can be attributed to an enhancement of the spin-current absorption. A theoretical model that considers both reflected and transmitted mixing conductances at the two interfaces of FM is developed to explain the results.